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 A261617 Numbers n such that n!!! + 3^n is prime. 0
 0, 2, 16, 17, 20, 22, 28, 31, 37, 40, 53, 65, 71, 73, 82, 124, 130, 187, 203, 266, 308, 326, 386, 502, 662, 1919, 3136, 3229, 4640, 8113, 8659, 12307, 20972, 26408, 49391 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS n!!! is the triple factorial sometimes written n!3. a(36) > 50000. LINKS Table of n, a(n) for n=1..35. EXAMPLE 2 is in the sequence because 2!!!+3^2 = 2+9 = 11 is prime. MATHEMATICA MultiFactorial[n_, k_] := If[n < 1, 1, If[n < k + 1, n, n*MultiFactorial[n - k, k]]]; Select[Range[0, 50000], PrimeQ[MultiFactorial[#, 3] + 3^#] &] CROSSREFS Cf. A007661, A124248, A124249, A261316. Sequence in context: A066773 A138761 A247634 * A075376 A032935 A004831 Adjacent sequences: A261614 A261615 A261616 * A261618 A261619 A261620 KEYWORD nonn AUTHOR Robert Price, Sep 09 2015 STATUS approved

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Last modified November 29 00:31 EST 2023. Contains 367422 sequences. (Running on oeis4.)